Combined mixer and intermediate frequency stage



s. HUNT 2,302,867 COMINED MIXER AND INTERMEDIATE FREQUENCY STAGE l Nov. 24, 1942.

Filed Oct. 25, 1941 INVENToR ArrRNEY SEYMOUR BY 7% Patent-ed Nov. 24, 1942 COMBINED MIXER AND INTRMEDIATE FREQUENCY STAGE Seymour Hunt, Flushing, N. Y., assgnor to Radio Corporation of America, a corporation of Dela- Ware Application october 25, 1941, serial No. 416,438 8 Claims. Cl. 250-20) accelerate the electron stream and to shield elec- This invention is concerned with an improvement in radio receivers of the superheterodyne type and more particularly with a combined first detector-oscillator or mixer and intermediate frequency stage that may be used with advantage in such receivers.

In the present state of the art it isknown to use in superheterodyne circuits a multi-electrode type of tube designed to perform simultaneously the functions of a mixer tube and of an oscillator tube. According to my present invention the same or equivalent multi-electrode tube is made to perform in addition the function of intermediate frequency amplification. As a result ne.- cessity for the use of a separate tube to perform the function of intermediate frequency amplication is dispensed with.

Other objects of the invention are to provide a circuit which would be attractive in small lowprice receiving sets where the cost must be kept down to a minimum; to provide a receiver'of reduced size and weight; and in battery-operated sets to provide economical operation by reducing battery consumption.

The novel features characteristic of my invention are set forth with particularity in the appended claims. 'I'he invention itself, however, both as to its organization and mode of operation. together with further objects and. advantages thereof, will best be understood by reference to the following description ltaken in connection with the accompanying drawing in which Fig. 1 and Fig. 2 illustrate preferred circuits embodying the present invention of combined mixer and intermediate frequency stages. n

vIn the circuit of Fig. 1, the tube designated V isa multi-electrode vacuum tube and may be of the type known as 6A7 or 6A8, also known as pentagrid converters. with a cathode K, an output or plate electrode P and a plurality ofy grids G1 .to G5 interposed in the space between K and P in the order named. In the normal use of this tube -as a pentagrid converter, the cathode K, rst grid G1 and second grid G2 have external circuit elements connected thereto to perform the function of a local oscillatorl for generating thel local oscillations, the grid G2 serving as the output or anode electrode of the oscillator. Received signal oscillations are impressed on the fourth grid G4, and due to the combined action within the tube oscillations of the Vintermediate frequency appear in the output circuit connected to the plate P. The third and fth grids G1 Gc are connected trostatically the signal control grid G4 from voltage fluctuations on the oscillator anode-grid G2 and the output anode P.

According to my invention the functions of the several electrodes and the connections theretol of the circuit elements are modified somewhat as will now be pointed out more particularly. In the circuit of Fig. 1 the grid G1 serves as the signal control grid as well as the oscillator grid.

` Connected between the signal grid G1 and cathposed between the antenna A and said resonant This tube is provided circuit L1--C1 through the radio frequency transformer T1. Included in the connection to the signal grid G1 is an inductance coil Lz to which there is coupled an inductance coil La, one end of the latter being connected'to the second grid G2 which serves as the oscillator anode, the other end of the coil Lsbeing connected to ground through a variable condenser C3. The circuit comprising the elements Ls-Cs constitutes the principal portion of a` circuit which is tuned to the oscillator frequency above or below the signal frequency by the amount of the intermediate frequency. The remaining portion of this circuit is vprovided by the primary tuned circuilt I1 of transformer T2 whichbeing tuned to the intermediate frequency presents a low reactance to the oscillator frequency. It will be seen therefore that the local oscillator is constituted by the electrodes K, G1 and G2 and that feedback from the output to the input of said oscillator is provided by the magnetic coupling between L2 and L3. VIt will be seen also that the grid G1 serves not only as the signal control grid for the received oscillations but also as the control grid of the local oscillator.

The variable tuning condensers C1 and C3, and the variable condenser C2 of the RF amplifier, if one is'used, are mechanically interconnected as shown by the dotted line U for the purpose of providing uni-control. Connected to the grid G2 is the approximately fixed tuned circuit I1 which is resonant to the intermediate frequency oscillations resulting from the interaction between the received signal oscillations and the locally generated oscillations. This `circuit is not exactly fixed tuned since the adjustment of C3 affects its resonant frequency, but if 'C3 is small compared to the capacity in I1,

together, v inside the tube envempe and serve tg this variation in tuning is not important. Couconstituted by the tuned intermediate frequency.

A fourth intermediate frequency circircuit I3. cuit I4 is coupled to the output circuit'Ia of tube. V, the coils of said circuits constituting the transformer Ts.

second intermediate frequency stage or else fed directly to a second detector, the resulting audio currents being fed to an audio frequency'amplier and reproduced by a loudspeaker in the usual manner.

In order to provide suitable operating bias for the signal control and oscillator grid G1 the cathode K has connected between it and ground the conventionalself-biasing resistancecapacity network, R-C. In the event that it is desired to provide the receiver with automatic volume control, the control bias therefor may be obtained in the usual manner from the second detector and fed either tothesignal grid G1 or the IF grid G4, or both. The electrodes G2, Ga-Gi, and P are connected to a suitable power supply source (not shown) vthrough the leads marked +B, +S and +B, respectively.

In the second embodiment of -my invention shown in Fig. 2 I make use of the tube V which combines in one bulb a triode and a pentode, these units being independent of each other except for the common cathode K. A representative type of tube that may be used is the 6FT or equivalent. The triode section of the tube includes the grid Git and the anode Pr. The pentode section includes grids G1P,Gzp, grid Gap, and the anode Pp. According to this embodiment of the invention the triode section'of the tube is designed to perform simultaneously the functions of local oscillator and mixer, and the pentode section serves as an intermediate frequency amplifier. Thereceived oscillations from the tuned circuit Li-Ci are fed to the triode grid Git. The circuit vlZ--Cs-Ii tuned to the frequency of the locally generated oscillations as explained previously is connected to the anode Pt and is coupled through the coils Lz--La to the grid Git. The resulting intermediate `frequency oscillations will appear in the circuit I1 which in turn is coupled to the circuit 12, the latter being connected to the first grid Gip of the pentode section. Amplification of the intermediate frequency occurs in the pentode section, the amplified oscillations appearing in the load circuit I3 connected to the plate Pp. In all other respects the circuits and functions of the various parts of the circuit shown in Fig. 2 are the same as described in connection with Fig. 1`.

While I have shown and described two preferred embodiments of the invention, it will be understood that modifications and changes may be made without departing from the spirit and scope of the invention, as will be understood by thoseskilled in the art.

What I claim is:

1. In a superheterodyne receiver, a circuit for performing the combined' vfunctions of first detector-oscillator and intermediate. 'frequency amplification, comprising van 'electrondischarge The oscillations occurring in the circuit I4 may then be further amplified a tube having within a common envelope a cathode, a plurality of grid electrodes and only two output electrodes, 'a tuned input circuit having impressed thereon the received signal oscillations connected between cathode and one of the grid electrodes, external circuit elements connected between said latter grid electrode, cathode and one of the output electrodes to serve as a generator of local oscillations, a rst intermediate frequency circuit connected to said one output electrode, a second intermediate frequency circuit coupled to the first intermediate `frequency circuit connected to one of the other grid electrodes, and a third intermediate frequency `circuit connected to the second output electrode.

2. A circuit as defined in claim l wherein the external circuit elements comprises an inductance coil connected to the grid electrode to which the signal input circuit is connected, a second coil in'coupledrrelation to the first connectedto said one output electrode, and a variable condenser connected to the second coil and forming therewith a tuned circuit resonant to the frequency of the locally generated oscillations.

3. In a superheterodyne receiver, a circuit for performing the combined functions of first detector-oscillator and intermediate frequency amplification, comprising an electron discharge tube having within a common envelope a cathode, a plurality of grid electrodes land a single anode electrode, a tuned input circuit having impressed thereon the received signal oscillations connected between cathode and -one of the grid electrodes, external circuit elements connected between said latter grid electrode, a second grid and cathode to -serve as a local oscillator, a first circuit tuned to the intermediate frequency oscillations resulting from the interaction between the received and local` oscillationsv connected to said second grid -electrode, Ia second circuit tuned to the intermediate frequency oscillations coupled to the first .intermediate frequency circuit and connected to a third grid electrode, and an output circuit also tuned to the intermediate frequency oscillations connected to the anode electrode. I

4. In a superheterodynereceiver, a circuitfvfo performing the combined functions of first detector-oscillator and intermediate frequency amplification, comprising an electron discharge tube having within la common envelope -a cathode, a single anode electrode and a'plurality of grid electrodes interposed in the space between cathode and the anode electrode, a tuned input circuit having impressed thereon the received signal oscillations connected 'between cathode and the first grid electrode next adjacent vthe cathode, a coil included in the connection between the input circuit and the first grid, a circuit having a coil in coupled relation to the first grid coil tuned Ato locally generated oscillations and connected 4between cathode and a second grid electrode, a first intermediate frequency circuit connected to said second grid electrode, a second intermediate frequency'circuit coupled to the first intermediate frequency circuit connected to a third grid electrode, and a third intermediate frequency circuit connected to the anode electrode. l

5. In a superheterodyne receiver, a circuit for performing the combined functions of first detector-oscillator and intermediate frequency amplification, comprising an electron discharge tube having within a common envelope electrodes constituting a triode and other electrodes constituting a pentode, the triode and pentode having a common cathode, a tuned input circuit having impressed thereon the received signal oscillations connected to the triode grid electrode, a circuit tuned to locally generated oscillations connected to the triode4 anode and being in coupled relation to the triode grid circuit, a first intermediate frequency circuit connected to the triode anode, a second intermediate frequency circuit coupled to the first intermediate frequency circuit connected to the signal grid electrode of the pentode, and a third intermediate frequency circuit connected to the pentode anode electrode.

6. A circuit as defined in claim 5 wherein an inductance coil is connected between the tuned input circuit and the triode grid electrode, and the circuit which is tuned to the locally generated oscillations comprises a variable condenser and a second inductance coil in coupled relation to the first coil.

7. In a superheterodyne receiver, a circuit for performing the combined functions of producing an intermediate frequency by mixing the received signal oscillations with locally generated oscillations and amplifying such intermediate frequency, comprising an electron discharge tube having within a common envelope a cathode and an anode electrode between which an electron stream is produced, a plurality of grid electrodes interposed in said electron stream between cathode and anode electrode, an input circuit tuned to the received signal oscillations connected between cathode and one of the grid electrodes, a coil included in the connection between the input circuit and said grid, a circuit tuned to locally generated oscillations connected between cathode and another grid electrode and having a coil in coupled relation to the first coil, a first intermediate frequency circuit connected to the latter grid electrode, a second intermedi-ate frequency circuit coupled to the rst intermediate frequency circuit connected to a third grid electrode, and a third intermediate frequency circuit connected to the anode electrode.

8. In a superheterodyne receiver, a circuit for performing the combined functions of producing an intermediate frequency by mixing the received signal oscillations with locally generated oscillations and the amplification of such intermediate frequency, comprising an electron discharge tube having within a common envelope a cathode and an anode electrode between which an electron stream is produced, a plurality of grid electrodes interposed in said electron stream between cathode and anode electrode, an input circuit tuned to the received signal oscillations connected between cathode and the first grid electrode next adjacent the cathode, a coil included in the connection between the input circuit and said first grid, a circuit having a coil in coupled relation to the first grid coil tuned to locally generated oscillations and connected between cathode and a second grid electrode, a rst intermediate frequency circuit connected to said second grid electrode, a second intermediate frequency circuit coupled to the first intermediate frequency circuit connected to a third grid electrode, and a third intermediate frequency circuit connected to the anode electrode.

SEYMOUR HUNT. 

